U.S. patent application number 12/981585 was filed with the patent office on 2011-04-21 for non-penetrating filtration surgery.
This patent application is currently assigned to I Optima Ltd.. Invention is credited to Ehud Assia, Alex Harel, Adi Shargil, Michael SLATKINE.
Application Number | 20110092965 12/981585 |
Document ID | / |
Family ID | 23293795 |
Filed Date | 2011-04-21 |
United States Patent
Application |
20110092965 |
Kind Code |
A1 |
SLATKINE; Michael ; et
al. |
April 21, 2011 |
NON-PENETRATING FILTRATION SURGERY
Abstract
Apparatus for ophthalmic surgery, especially non-penetrating
filtration surgery, comprising a laser source that ablates sclera
tissue at steps of intermediate thickness. Optionally, the beam is
scanned using a scanner and its results viewed using an ophthalmic
microscope.
Inventors: |
SLATKINE; Michael; (Herzlia,
IL) ; Assia; Ehud; (Tel-Aviv, IL) ; Harel;
Alex; (Savyon, IL) ; Shargil; Adi; (Natania,
IL) |
Assignee: |
I Optima Ltd.
Ramat-Gan
IL
|
Family ID: |
23293795 |
Appl. No.: |
12/981585 |
Filed: |
December 30, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10495649 |
Dec 16, 2004 |
7886747 |
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PCT/IL02/00872 |
Nov 3, 2002 |
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12981585 |
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PCT/IL00/00263 |
May 8, 2000 |
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10495649 |
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60331402 |
Nov 15, 2001 |
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Current U.S.
Class: |
606/5 |
Current CPC
Class: |
A61F 9/00802 20130101;
A61F 2009/00872 20130101; A61F 9/00825 20130101; A61F 2009/00868
20130101; A61F 2009/00865 20130101; A61F 9/00821 20130101; A61F
2009/00897 20130101; A61F 2009/00891 20130101 |
Class at
Publication: |
606/5 |
International
Class: |
A61B 18/20 20060101
A61B018/20 |
Claims
1. Apparatus for ophthalmic surgery on an eye comprising: a laser
source that generates a laser beam having a wavelength; and an
ophthalmicly effective position controller adapted to aim said beam
at said eye from outside said eye for a dwell time and a power
density configured to ablate a sclera tissue thickness of between 5
and 50 microns in a single dwell.
2. Apparatus according to claim 1, wherein said thickness is
between 5 and 30 microns.
3. Apparatus according to claim 1, wherein said laser source and
said position controller are configured so that said ablation is
without causing substantial shockwave or thermal damage to said
eye.
4. Apparatus according to claim 1, wherein said beam contacts said
eye for a dwell time of above 100 micro-seconds, per dwell.
5. Apparatus according to claim 1, wherein said beam contacts said
eye with a spot size of over 100 microns.
6. Apparatus according to claim 1, comprising an ophthalmic
microscope operative to view an eye during an ophthalmic procedure
that uses said laser beam.
7. Apparatus according to claim 6, comprising a monitor for
displaying a view of said tissue removal viewed by said
microscope.
8. Apparatus according to claim 6, comprising a beam combiner for
combining a line of sight of said laser and said microscope.
9. Apparatus according to claim 8, comprising an optical system
integral with said combiner and configured to allow manual
adjustment of a focus of said laser source so that it is in a same
plane as the focus of said microscope.
10. Apparatus according to claim 1, wherein said position
controller comprises an ophthalmic frame operative to fix a
relative position and angle of said laser source and an eye of a
patient.
11. Apparatus according to claim 1, wherein said position
controller comprises a scanner comprising an input for said laser
beam and an output of a spatially scanned laser beam.
12. Apparatus according to claim 11, comprising controlling
circuitry that drives said scanner to remove tissue in a desired
pattern on the eye, said pattern being suitable for non-penetrating
filtration surgery on the eye.
13. Apparatus according to claim 12, wherein said pattern has
dimensions of between 2 and 5 mm in each of two orthogonal
axes.
14. Apparatus according to claim 12, wherein said circuitry
controls said laser source.
15. Apparatus according to claim 12, wherein said circuitry drives
said scanner to coagulate tissue using said laser source.
16. Apparatus according to claim 12, wherein said circuitry drives
said scanner to ablate tissue in an adjustable thickness.
17. Apparatus according to claim 12, wherein said circuitry drives
said scanner to perform said ablation by causing repeated ablations
of thicknesses at a location, which repeated ablations add up to
said thickness.
18. Apparatus according to claim 12, wherein said circuitry drives
said scanner to ablate tissue at a location only after a delay from
a previous ablation thereat, said delay being configured to be
sufficient to detect percolation thereat.
19. Apparatus according to claim 12, comprising an aiming beam
laser source and wherein said circuitry drives said scanner to show
said pattern boundaries using said aiming beam.
20. Apparatus according to claim 12, comprising a sensor which
monitors an indication of progression of said surgery, on said eye,
to produce a progression signal.
21. Apparatus according to claim 20, wherein said sensor comprises:
a camera which acquires an image of said tissue removal; and an
image processor that processes said image.
22. Apparatus according to claim 20, comprising circuitry that uses
said progression signal to generate an indication of the tissue
removal state.
23. Apparatus according to claim 22, wherein said circuitry uses
said indication to close a control loop of said tissue removal.
24. Apparatus according to claim 22, wherein said indication of
tissue removal state comprises an indication of the thickness of
remaining tissue in the area of tissue removal.
25. Apparatus according to claim 22, wherein said indication of
tissue removal state comprises an indication of a percolation rate
through the remaining tissue in the area of tissue removal.
26. Apparatus according to claim 20, wherein said sensor is a
non-penetrating sensor.
27. Apparatus according to claim 20, wherein said sensor is a
contact sensor.
28. Apparatus according to claim 20, wherein said controlling
circuitry receives signals from said sensor.
29. Apparatus according to claim 20, comprising a user input,
wherein said controlling circuitry is adapted to receive and
interpret entries on said input as indicating signals from said
sensor.
30. Apparatus according to claim 1, comprising a frame attached to
said combiner, which frame blocks said laser beam from at least one
part of said eye.
31. Apparatus according to claim 1, wherein said wavelength has an
absorption length of 1/e of greater than 5 microns in water.
32. Apparatus according to claim 1, wherein said laser source
comprises a CO2 laser source.
33. Apparatus according to claim 1, wherein said laser source
comprises an isotopic 13C16O2 laser source.
34. Apparatus according to claim 1, wherein said laser source
comprises an Erbium:YSGG laser source.
35. Apparatus according to claim 1, wherein said laser source
comprises a diode laser source.
36. Apparatus according to claim 1, wherein said laser source
comprises a UV laser source.
37. Apparatus according to claim 1, wherein said laser source
generates a second, visible wavelength, aiming beam aligned with
said laser beam.
38. Apparatus according to claim 1, wherein said laser beam is a
pulsed laser, each pulse corresponding to a single dwell.
39. Apparatus according to claim 1, wherein said laser beam is a
pulsed laser, a plurality of pulses being grouped for a single
dwell.
40. Apparatus according to claim 1, wherein said laser beam is a
continuous laser that is artificially gated to generate shots.
41. Apparatus according to claim 38, wherein said dwell time is
over 1 milliseconds.
42. Apparatus according to claim 11, wherein said circuitry is
configured to remove sclera tissue in the shape of a reservoir
suitable for non-penetrating trabeculectomy.
43. Apparatus according to claim 11, wherein said circuitry is
configured to remove sclera tissue in the shape of a percolation
area suitable for non-penetrating trabeculectomy.
44. Apparatus according to claim 43, wherein said forming includes
removing in a concave pattern.
45. Apparatus according to claim 1, wherein said beam has a power
of over 5 watts.
46. Apparatus according to claim 1, wherein said beam has an energy
density of between 3 and 20 J/cm.sup.2, per dwell.
47. Apparatus according to claim 1, wherein said laser ablates
between 10 and 30 microns in a single dwell.
48. Apparatus according to claim 1, wherein said laser ablates
between 16 and 25 microns in a single dwell.
49. Apparatus according to claim 1, wherein said laser ablates
between 16 and 20 microns in a single dwell.
Description
RELATED APPLICATIONS
[0001] This application is a divisional of pending U.S. patent
application Ser. No. 10/495,649 filed on Dec. 16, 2004, which is a
National Phase of PCT Patent Application No. PCT/IL02/00872 filed
on Nov. 3, 2002, which claims the benefit under 35 USC.sctn.119(e)
of U.S. Provisional Patent Application No. 60/331,402 filed on Nov.
15, 2001.
[0002] PCT Patent Application No. PCT/IL02/00872 is also a
continuation-in-part (CIP) of PCT Patent Application No.
PCT/IL00/00263 filed on May 8, 2000, now U.S. patent application
Ser. No. 10/240,505 filed on Sep. 30, 2002, issued as U.S. Pat. No.
7,135,016 on Nov. 14, 2006.
[0003] The disclosures of all of the above applications are
incorporated herein by reference.
FIELD OF THE INVENTION
[0004] The present invention is related to the field of Glaucoma
treatment using laser ablation.
BACKGROUND OF THE INVENTION
[0005] Glaucoma is an optical neuropathy associated with increased
intraocular pressure. The mechanism of the disease is not fully
understood. However, the most effective therapy appears to be
reducing the intraocular pressure, for example using medication or
implants. Further damage to the optic nerve is thus prevented or
reduced.
[0006] One procedure that has been suggested is non-penetrating
trabeculectomy, in which a portion of the sclera overlying the
Schlemm's canal is removed, allowing aqueous humor to leave the
eye. It is desirable to remove only part of the thickness of the
sclera, preventing penetration into the eye. However, this
procedure is difficult to perform with a knife. Typically, the
effect of the procedure can only be gauged after a while, since
intra-ocular pressure is only measured after the procedure is
completed. As the pressure of the knife causes trauma to the eye,
the pressure is not usually measured until the eye has somewhat
recovered, such as the next day. In laser based procedures, such as
SLT and ALT, pressure is sometimes measured after the procedure is
completed, to ensure that the intra-ocular pressure did not
suddenly rise.
[0007] U.S. Pat. No. 5,370,641 to O'Donnell, the disclosure of
which is incorporated herein by reference, describes using an
Excimer laser or an Erbium laser to ablate the sclera overlying the
Schlemm's canal and the trabecular meshwork thereby forming a
porous membrane. The laser spot size and treatment area are not
described. This patent states that when a sufficient amount of the
corneoscleral bed is removed, aqueous humor comes through the
remaining ultra-thin Schlemm's canal and trabecular meshwork and
the energy of the laser is absorbed by the out-flowing humor,
creating a self-regulating end point.
[0008] However, even though many years have passed since this
patent was issued, the method taught in the patent has not found
wide-spread use, in spite of a great need in the art of treating
Glaucoma, a disease for which there is no completely satisfactory
treatment. One possible reason is that the '641 patent uses lasers
that remove very thin (micron sized) layers of material. Further,
once even a weak percolation starts, the laser is only effective to
remove the percolation, not further tissue, while at the same time
possibly causing thermal damage to the underlying tissue. This
thermal damage may be a cause of later scarring.
SUMMARY OF THE INVENTION
[0009] An aspect of some embodiments of the invention relates to
apparatus for effecting and controlling a non-penetrating
filtration procedure, using an ablation source that remove a layer
of tissue of intermediate thickness, for example, between 5 and 30
microns. In an exemplary embodiment of the invention, the ablation
source and parameters are selected so that the removal depth is
smaller than a desired final membrane thickness but greater than a
thickness of percolation which may be expected prior to the desired
membrane thickness being achieved. In an exemplary embodiment of
the invention, the ablation source is absorbed by the percolation.
Optionally, the ablation parameters are selected so that the
process of ablation is self-curtailed when the percolation is fast
enough to create a layer the thickness of the ablation depth. In an
exemplary embodiment of the invention, the ablation source is
selected to have the flexibility to provide more than one
meaningful ablation depth.
[0010] In an exemplary embodiment of the invention, the laser is a
diode laser operating at 1.8 microns, a .sup.13C.sup.16O.sub.2
isotope laser or an Erbium:YSGG laser. In contrast to Erbium:YAG
lasers, for example, the above listed lasers have an ablation depth
that is greater than the small ablation depth of 1-3 microns of the
Erbium:YAG laser. This is also the percolation thickness which may
be expected to exist, in many cases, long before the membrane is
thin enough. While the thickness of the percolation is dependent on
the time between pulses, practical reasons, such as laser pulse
rate, thermal damage and shock wave damage potentially caused by
the laser pulse transfer generally prevent the practical use of low
(e.g., micron) ablation depth lasers such as the Excimer and Er:YAG
for the application of ablation. It should be noted that in the
field of skin resurfacing, the standard (non isotopic)
.sup.12C.sup.16O.sub.2 laser rules supreme. While this laser does
have some degree of flexibility the minimum ablation depth (where a
minimum of charring is produced) is about 30 to 50 microns, which
may not be fine enough for some patients and/or protocols. In
addition, it should be noted that unlike in skin applications,
thermal damage to the membrane and/or other eye tissue does not
heal as readily and is more likely to scar, for example due to the
lack of underlying healing tissue.
[0011] In an exemplary embodiment of the invention, the apparatus
includes a scanner for automatically scanning an area of the eye
using a laser spot, thereby ablating over the entire area.
Optionally, a continuous scan is used, with the laser beam on at
all times. A potential advantage of using a scanner is the ability
to provide a large total amount of energy to a large area of the
eye using a relatively inexpensive laser and scanning the beam over
the area. Optionally, a pulsed .sup.13C.sup.16O.sub.2 laser such as
an ultrapulse laser with a scanner, for example, a galvanometric
scanner, is used.
[0012] Another potential advantage of using a scanner is that a
uniform percolation profile (or another desired profile) may be
achieved. Optionally, a uniform final tissue thickness is created
by the ablation. Alternatively, different tissue types or areas may
have different thickness, so that a uniform percolation is
achieved. In some cases, the ablated sclera or cornea thickness
will vary responsive to the underlying tissue. In some embodiments
of the invention, the desired percolation rate is a factor that
controls the process and/or ablation parameters.
[0013] In some embodiments of the invention, a reservoir is ablated
in the sclera and/or cornea for collecting the percolating aqueous
humor.
[0014] In one embodiment of the invention, the laser beam is
optically combined with a visual system, using an optical combiner,
to allow monitoring of the procedure. Optionally, the visual system
is a ophthalmic microscope, for viewing the area of ablation by a
physician performing the procedure. Alternatively or additionally,
the visual system is an automatic vision system. Optionally, the
optical combiner comprises a micro-manipulator, allowing the
physician to change the laser aiming point and/or scan area. It is
noted that standard micro-manipulators and beam combiners do not
support an input from a spatially scanning laser beams.
[0015] An advantage of monitoring using a human or automatic visual
system is that the ablation at a particular location on the eye can
be stopped as soon as the aqueous humor starts percolating out,
without requiring an optional self-limiting behavior of the a laser
beam to take effect.
[0016] An aspect of some embodiments of the invention relates to
using a sensor, for example, an automatic vision system for
monitoring a non-penetrating filtration procedure. In one
embodiment of the invention, the vision system detects percolation
of liquid from the ablated sclera or cornea, thus identifying that
ablation at the percolating point should be stopped. Optionally,
this allows a greater degree of safety. Alternatively or
additionally, the vision system controls the scanner (or laser) to
reduce or eliminate the scanning of the laser at some points, while
continuing the scanning at other points in the eye.
[0017] In an alternative embodiment of the invention, a pressure
sensor is used to measure an intra-ocular pressure, during and/or
after a procedure. The measurement may be, for example, continuous
or intermittent. The measurement may be performed during pauses in
the procedure and/or may be performed while the procedure
continues. In some cases, for example, if the pressure goes down
this may indicate a successful percolation. If the pressure does
not go down enough, this may indicate that a larger area should be
ablated. If the pressure goes down too much, possibly the procedure
should be stopped at once. This sensor may be coupled to the system
to operate automatically. For example, an input from the sensor may
be used to automatically stop or change ablation parameters.
Alternatively, the sensor is used to generate an alarm, through the
ablation system or on its own (e.g., by setting a pressure at which
to sound an alarm). Alternatively or additionally, the sensor is
used manually, for example, with a physician entering new ablation
parameters into the ablation system (e.g., using a suitable input)
based on the pressure reading and/or entering pressure values which
are interpreted by the ablation system to change its
parameters.
[0018] Alternatively or additionally to using a pressure sensor, an
ablation thickness sensor or a sclera thickness sensor is used to
determine if ablation is to continue and/or under what
parameters.
[0019] In an exemplary embodiment of the invention, the pressure
sensor is a non-penetrating sensor that optionally contacts the
outside of the eye. Alternatively, a penetrating pressure sensor is
used, for example, as part of a system that penetrates the eye and
controls the intra-ocular pressure by providing or removing fluid,
as needed.
[0020] An aspect of some embodiments of the invention relates to an
eye protector. In an exemplary embodiment, the eye protector
prevents ablation by the laser outside of a pre-defined area, for
example by physically blocking the laser light. Optionally, the eye
protector is adhesive to the eye. Alternatively or additionally,
the eye protector maintains open, during the procedure, one or more
flaps formed in the eye. Alternatively or additionally, the eye
protector is disposable.
[0021] There is thus provided in accordance with an exemplary
embodiment of the invention, apparatus for ophthalmic surgery on an
eye comprising:
[0022] a laser source that generates a laser beam, adapted to
ablate a scleral tissue thickness of between 5 and 30 microns in a
single shot; and
[0023] an ophthalmicly effective position controller. Optionally,
the apparatus comprises an ophthalmic microscope operative to view
an eye during an ophthalmic procedure that uses said laser beam.
Optionally, the apparatus comprises a monitor for displaying a view
of said tissue removal viewed by said microscope. Alternatively or
additionally, the apparatus comprises a beam combiner for combining
a line of sight of said laser and said microscope.
[0024] In an exemplary embodiment of the invention, said position
controller comprises an ophthalmic frame operative to fixing a
relative position and angle of said laser source and an eye of a
patient. Alternatively or additionally, said position controller
comprises a scanner comprising an input for said laser beam and an
output of a spatially scanned laser beam. Optionally, the apparatus
comprises controlling circuitry that drives said scanner to remove
tissue in a desired pattern on the eye. Optionally, the apparatus
comprises a sensor which monitors an indication of progression of
said surgery, on said eye, to produce a progression signal.
Optionally, the apparatus comprises:
[0025] a camera which acquires an image of said tissue removal;
and
[0026] an image processor that processes said image. Alternatively
or additionally, the apparatus comprises circuitry that uses said
progression signal to generate an indication of the tissue removal
state. Optionally, said circuitry uses said indication to close a
control loop of said tissue removal. Alternatively or additionally,
said indication of tissue removal state comprises an indication of
the thickness of remaining tissue in the area of tissue removal.
Alternatively or additionally, said indication of tissue removal
state comprises an indication of a percolation rate through the
remaining tissue in the area of tissue removal.
[0027] In an exemplary embodiment of the invention, said sensor
measures an intra-ocular pressure. Alternatively or additionally,
said sensor is a non-penetrating sensor. Alternatively or
additionally, said sensor is a contact sensor.
[0028] In an exemplary embodiment of the invention, said
controlling circuitry receives signals from said sensor.
[0029] In an exemplary embodiment of the invention, the apparatus
comprises a user input, wherein said controlling circuitry is
adapted to receive and interpret entries on said input as
indicating signals from said sensor.
[0030] In an exemplary embodiment of the invention, the apparatus
comprises a frame attached to said combiner, which frame blocks
said laser beam from at least one part of said eye.
[0031] In an exemplary embodiment of the invention, said laser
source comprises a CO.sub.2 laser source.
[0032] In an exemplary embodiment of the invention, said laser
source comprises an isotopic .sup.13C.sup.16O.sub.2 laser
source.
[0033] In an exemplary embodiment of the invention, said laser
source comprises an Erbium:YSGG laser source.
[0034] In an exemplary embodiment of the invention, said laser
source comprises a diode laser source operated at a wavelength near
1.8 microns.
[0035] In an exemplary embodiment of the invention, said laser
source comprises a UV laser source.
[0036] In an exemplary embodiment of the invention, said laser
source generates a second, visible wavelength, aiming beam aligned
with said laser beam.
[0037] In an exemplary embodiment of the invention, said laser beam
is a pulsed laser, each pulse being a single shot. Alternatively,
said laser beam is a pulsed laser, a plurality of pulses being
grouped as a single shot. Alternatively, said laser beam is a
continuous laser that is artificially gated to generate shots.
[0038] There is also provided in accordance with an exemplary
embodiment of the invention, a method of performing a
non-penetrating filtration procedure, comprising:
[0039] opening a flap in an eye, overlying a Schlemm's canal of
said eye;
[0040] forming a percolation zone adjacent said Schlemm's canal by
ablation using a laser that ablates a tissue thickness of between 5
and 30 microns, each shot;
[0041] forming a reservoir in a sclera of said eye and in fluid
connection with said percolation zone; and
[0042] closing said flap. Optionally, forming a percolation zone
comprises cleaning away charred tissue from said percolation zone.
Alternatively or additionally, the method comprises forming by
automatic scanning with a laser. Optionally, automatic scanning
with a laser comprises automatically controlling at least one
parameter of the scanning responsive to an effect of the laser on
the tissue.
[0043] In an exemplary embodiment of the invention, said laser is a
CO.sub.2 laser. Alternatively, said laser is a
.sup.13C.sup.16O.sub.2 laser. Alternatively, said laser is an
Er:YSGG laser. Alternatively, said laser is a diode laser operated
near 1.8 microns wavelength.
[0044] In an exemplary embodiment of the invention, the method
comprises placing a protective sticker on said eye prior to forming
said percolation zone, said protective sticker having a spatial
window that admits a wavelength of said laser and a body that block
said wavelength from parts of the eye other than an area to be
ablated.
[0045] There is also provided in accordance with an exemplary
embodiment of the invention, a method of performing a
non-penetrating filtration procedure, comprising:
[0046] forming a percolation zone adjacent a Schlemm's canal of an
eye
[0047] measuring an intra-ocular pressure of said eye in response
to said forming a percolation zone; and
[0048] modifying parameters of said forming in response to said
measuring.
BRIEF DESCRIPTION OF THE FIGURES
[0049] Exemplary, non-limiting embodiments of the invention will be
described below, with reference to the following figures, in which
the same elements are marked with the same reference numbers in
different figures:
[0050] FIG. 1 is a schematic illustration of an exemplary
ophthalmologic ablation system, during a non-penetrating filtration
procedure in accordance with an exemplary embodiment of the
invention;
[0051] FIGS. 2A-2C illustrate the absorption of laser energy by
sclera tissue, for three different types of laser source;
[0052] FIG. 2D is a graph showing the relative utility of lasers
for sclera surgery, in accordance with an exemplary embodiment of
the invention;
[0053] FIG. 3A is a schematic illustration of an exemplary scanner
suitable for the system of FIG. 1;
[0054] FIG. 3B is a schematic illustration of an exemplary micro
manipulator for the system of FIG. 1, in accordance with an
exemplary embodiment of the invention;
[0055] FIG. 4 is a flowchart of a method of non-penetrating
filtration, in accordance with an exemplary embodiment of the
invention;
[0056] FIG. 5 is a perspective view of an eye showing an exposed
ablation area, in accordance with an exemplary embodiment of the
invention;
[0057] FIGS. 6A and 6B illustrate a completed percolation and
reservoir system, from a side and a top view, in accordance with an
exemplary embodiment of the invention;
[0058] FIG. 7 illustrates an exemplary protective framework, in
accordance with an embodiment of the invention; and
[0059] FIGS. 8A and 8B illustrate two alternative exemplary eye
protectors in accordance with some embodiments of the
invention.
DETAILED DESCRIPTION OF SOME EMBODIMENTS
[0060] FIG. 1 is a schematic illustration of an exemplary
ophthalmologic ablation system 50, during a non-penetrating
filtration procedure in accordance with an exemplary embodiment of
the invention.
[0061] Referring first to an eye 40, an exemplary filtration
procedure using system 50 comprises ablating parts of an area 31 of
a sclera 41 and/or a cornea 42 in an area 30. Some of the ablation
is directed to those areas overlying a Schlemm's canal 34 and/or
trabecular meshwork 32. The size of area 30 is exaggerated in FIG.
1, as in many procedures, area 30 is significantly smaller than
area 31 and may comprise substantially only the boundary area
between cornea 42 and sclera 41 that overlies the Schlemm's canal.
In some procedures, however, a larger portion of the cornea may be
ablated. Optionally, a scanner is used to scan a laser spot over an
area of the sclera larger than the spot. A more detailed
description of an exemplary filtration procedure and an exemplary
scanner is provided below. Also shown are optional sensors 35, 37
and/or 39, described below.
[0062] The thickness of sclera tissue at area 30 prior to ablation
is, for example, 1 mm. The desired thickness of the sclera after
ablation is, for example, between 10 microns and 50 microns. It
should be noted that it is desired that a complete membrane of
sclera tissue be maintained, to reduce complications caused by
entering the eye itself.
[0063] Laser ablation operates by light being absorbed by tissues
in a thin layer, for example between 1 and 50 microns thick and the
light causing heating of the tissue, so that the absorbing tissue
explodes. This explosion can also cause (generally unwanted) damage
by means of a shockwave produced by the explosion or by heat that
is absorbed by underlying and/or adjacent tissue. When the membrane
is thin enough, fluid percolates through the membrane and covers
it. This fluid is generally very similar to the sclera tissue,
especially with regard to optical absorption and heat dissipation
properties. Thus, the fluid ablates in much the same way and
parameters as sclera tissue. As can be expected, each type of laser
wavelength has different interaction parameters with the sclera
tissue and has further functional limitations caused by the
physical limitations of the laser, for example commercially viable
power level and pulse rate.
[0064] It has now been determined that different types of lasers
have different utilities when used for ablation of the sclera and
for non-penetration filtration. In particular, two properties of
the laser may be of interest. First, the depth of ablation, which
determines how large a thickness is ablated at one time and,
second, the matching between the fluid ablation and the sclera
ablation.
[0065] In some cases, an interesting result of these two
properties, self-limiting of ablation, can be achieved. For
example, if a laser has a given ablation depth and the fluid has
the same ablation properties as the sclera and the local pulse rate
of the laser is low enough to allow fluid to percolate to the
ablation thickness, repeated laser pulses will only remove (the
self renewing) fluid and not further ablate the sclera. In some
cases, however, this self-limiting behavior can be self defeating
or meaningless. FIGS. 2A-2C show the effects of various types of
laser on sclera tissue.
[0066] FIG. 2A shows the situation where a highly absorbed laser,
such as Erbium:YAG is used. Reference 43 indicates the amount of
fluid that percolated through a membrane 48 since the laser pulse.
Reference 44 indicates the area that can be ablated by a single
Erbium:YAG laser pulse. As can be seen, the ablation of membrane 48
cannot continue if fluid 43 percolates faster than the pulse rate.
The effective pulse rate is moreover limited by the damage caused
by shockwave of the laser and by the laser itself which has a
limited pulse rate. If scanning is desired, this further limits the
effective pulse rate of the laser, in as much as percolation from
adjoining areas may also cover the ablated area.
[0067] FIG. 2B shows the situation where a low absorption laser is
used, for example, a .sup.12C.sup.16O.sub.2 laser. This laser is
characterized by a large ablation depth 44 (e.g., 30-50 microns as
opposed to 1-3 microns of an Erbium:YAG laser) and also a large
thermal damage depth 46. Thus, in the configuration shown, the
small amount of percolation does not prevent a large thickness of
sclera from being ablated. However, the remaining sclera is likely
to be thermally damaged. Also, it is difficult to fine tune the
exact thickness of membrane 48, in as much as the depth of ablation
is so large. Thus, the percolation rate, which is dependent on the
thickness of membrane 48, is more difficult to exactly achieve. In
fact, the self-limiting point may be skipped by the laser
inadvertently ablating clear through the sclera. In many cases,
however, even such rough approximation may be good enough, for
example, by ablating different thickness of membrane over different
parts of the eye, so that the total effective (e.g., averaged)
percolation rate is as desired, while taking care to not
over-ablate the sclera and penetrate the eye. Alternatively or
additionally, the local pulse rate may be selected to be low enough
(e.g., by modifying the pulse rate and/or scanning pattern) so that
a sufficiently thick layer of fluid 43 percolates and serves to
control the amount of actual sclera tissue ablated.
[0068] FIG. 2C shows the situation where an intermediate absorption
laser is used, for example, an isotopic .sup.13C.sup.16O.sub.2
laser, an Erbium:YSGG or a diode laser at 1.8 microns wavelength.
The thickness of ablation and of thermal damage is relatively
small, especially relative to a final desired membrane thickness,
but still greater than percolation that occurs when the membrane is
not at its target thickness. It should be noted that there may be a
variation in percolation rate between patients and/or intra-ocular
eye pressures, so that even if a same membrane thickness and/or
percolation properties are desired, different fluid percolation
rates may be observed during the procedure.
[0069] FIG. 2D is a graph showing the relative utility of lasers
for sclera surgery, in accordance with an exemplary embodiment of
the invention. the different lasers are compared using a unit N
which indicates thickness of membrane 48 in units of minimum
ablation thickness of the laser. The thickness of membrane 48 is
taken to be 100 microns, thus, N=(100 microns/ablation thickness).
If a different thickness is selected, different values of N will be
generated. A more exact presentation of N and the ablation depth
(based on a minimum or typical penetration depth that provided
effective ablation) is shown in a table below. The one sided
"error" bars indicate the depth of thermal damage to be expected.
Two bands are marked on the figure. The shaded band indicates a
range of values for N which apparently afford control while
allowing a desired ablation to be performed. The dotted lines
enclose a wider band where control is marginal but may be suitable
for various applications. In general, as N is larger, finer control
can be achieved, but procedure time is longer and is in danger of
being limited by non-final percolation. As N is smaller, less
control but surer ablation can be achieved. For some lasers, it is
possible to control the penetration depth by modifying the pulse
duration and/or the energy of the pulse. However, many lasers are
limited by the physical properties of the laser and/or the degree
of control is not sufficient to allow a laser that is not useful to
become useful.
[0070] As can be appreciated, these indications are not absolute.
For example, if the desired membrane thickness is greater, lasers
with a currently low N may become more useful. Lasers with a high
N, however, suffer from being self limiting when there is
percolation, thus, to be effective, the laser must be able to
provide multiple pulses in the time it takes for percolation the
thickness of the ablation depth to occur, if this percolation is
not the desired final effect. Also, some method of preventing
damage from shockwave and other artifacts may be required. Thus,
other useful values of N (for a 100 micron thickness) are below 50,
20, 10 and 6 and/or above 2, 3, 4, 5, 7 and 10. In general, a
useful value of N for any thickness may depend on the precision
desired in setting the thickness, so the above listed possibly
useful values of N may apply to an N calculated using a different
membrane thickness.
[0071] As can be seen, Erbium:YAG and Excimer lasers have too small
an ablation thickness, while .sup.12C.sup.16O.sub.2 is marginal and
Ho:YAG has too large an ablation thickness. Diode lasers operated
at 1.8 micron wavelength, Erbium:YSGG and isotopic
.sup.13C.sup.16O.sub.2 operated at 11.2 microns wavelength have an
intermediate ablation thickness which allows for freedom in
manipulating the thickness (e.g., by increasing the energy) and
more exact approximation of the final membrane thickness, even
under conditions of partial percolation. Other lasers may be used
as well, if they have spectral characteristics (and/or absorbency
characteristics) that match the areas and lines shown in FIG.
2D.
TABLE-US-00001 Penetration depth in water (1/e) = approximate N
(for thickness Laser Type ablation depth of 100 microns) Excimer 1
micron 100 Diode at 1.8 micron 20 microns 5 Holmium:YAG 100-200
microns 1-0.5 Er:YSGG 15 micron 7 Er:YAG 1-3 micron 100-30
.sup.12C.sup.16O.sub.2 30-50 micron 2-3 .sup.13C.sup.16O.sub.2 15
micron 7
[0072] Alternatively, a laser may be selected that has a low
absorption in the percolating fluid, and an intermediate or high
absorption in the sclera tissue. However, this laser may not have
the desired self-limiting effect. Alternatively, a combination of
laser wavelengths may be used.
[0073] The laser source is shown in FIG. 1 as a laser source
52.
[0074] The type of interaction of the laser (or other light) with
the eye is typically that of ablation, especially low-char
ablation. However, other tissue removing interactions may be used
as well, for example, vaporization and coagulation (and then
optionally removal of the damaged tissue).
[0075] Optionally, source 52 also generates an aiming laser beam
(not shown), having a low power and/or being visible. The aiming
beam is optionally coaxial with ablation beam 54. This aiming beam
may be formed by a separate laser boresighted with beam 54.
[0076] In one embodiment of the invention, laser beam 54 has a spot
size smaller than the size of area 30 that is actually ablated.
Beam 54 is optionally scanned over area 30 using a scanner 56, for
example a mechanical, electro-optical or acusto-optical scanner. An
exemplary scanner is described in greater detail below.
[0077] In some embodiments of the invention, the procedure is
monitored through an ophthalmic microscope 58 or other suitable
optical instrument. In one embodiment of the invention, a human
viewer 62 views area 30 though an eyepiece 60 of microscope 58.
Alternatively or additionally, the procedure is imaged using an
imager 64, such as a CCD camera.
[0078] In an exemplary embodiment of the invention, beam 54 (and/or
optional the optional aiming beam) is optically combined with the
line of sight of microscope 58 and/or that of imager 64, using a
beam combiner 70. Optionally, combiner 70 comprises a
micro-manipulator, allowing the relative location of beams 54 and
the line of sight of microscope 58 to be modified. Various types of
micro-manipulators may be used, with a particular one being
described below. In an exemplary embodiment, a joy stick 72 is
provided on beam combiner 70 to control the relative lines of
sight.
[0079] Unlike standard beam-combiners for ophthalmic use, combiner
70 is expected to receive a scanning beam, rather than a point
source. Thus, the optics of combiner 70 are optionally designed to
correctly aim the beam over a significant range of beam positions,
such as .+-.2, .+-.4 or .+-.5 mm off center of the
micro-manipulator input axis.
[0080] The image (or image sequence) acquired by imager 64 may be
used in various ways. In one embodiment of the invention, the
acquired image may be displayed, for example using a display 66.
Alternatively or additionally, the acquired image is recorded.
Alternatively or additionally, the acquired image is analyzed using
an image processor 68. In some embodiments, the image and/or
control parameters are transmitted to a remote location, such as
using an Internet or other communication network.
[0081] In some embodiments of the invention, the image analysis is
used to detect the percolation of aqueous humor. Alternatively or
additionally, the image processing confirms that ablation beam 54
(or the aiming beam) are within a designated safety area.
Alternatively or additionally, the image processing detects the
depth of ablation, for example using stereoscopic images, by shadow
analysis and/or by virtue of thin tissue being more transparent.
The thickness of the tissue may be then determined, for example, by
shining a strong light into the eye and measuring the relative or
absolute amount of light exiting through the ablated tissue.
Optionally, dye is provided into the eye, for example using
iontophoresis (or injection) and the degree of percolation is
determined by viewing the color intensity of the percolating
aqueous humor.
[0082] The detected percolation may be used to provide feedback to
the treating physician, for example using display 66 or via an
audio alarm (not shown). Alternatively or additionally, laser 52
may be shut off or beam 54 blocked, for example at scanner 56 or
combiner 70. Alternatively or additionally, the image processing
results may be used to complete a control loop, such as by
controlling the scanning parameters of scanner 56.
[0083] In some cases, the laser beam may inadvertently penetrate
into the eyeball. Optionally, such penetration is detected based on
a flow rate of aqueous humor from the eye (which is a typically
higher rate than that provided by percolation). Optionally, the
procedure may be completed as a penetrating filtration procedure.
Alternatively or additionally, a penetration is planned at at least
one part of the eye. Optionally, the scanner is controlled to
congeal and/or scar the tissue at or near the penetration area.
[0084] In one embodiment of the invention, a controller 74 is
provided to receive the image processing results and apply suitable
control to laser source 52, scanner 56, combiner 70. Alternatively
or additionally, controller 74 is used for processing and
displaying of data and/or for receiving input from the treating
physician, such as procedure parameters. An suitable input device
76 may be provided.
[0085] FIG. 3A is a schematic illustration of an exemplary scanner
56 suitable for system 50. A beam 54 from laser source 52 is
scanned in a first axis by a mirror 100, powered by a motor 102. A
second mirror 104, powered by a second motor 106 scans the beam in
another, optionally orthogonal axis. The two mirrors may be
controlled by a scanning controller 108. The scanning is optionally
continuous over a defined scanned area. In some embodiments, a same
scanner may be used for scanning different sized and shaped areas.
A beam attenuator 110 is optionally provided to selectively
attenuate beam 54, for particular scanned locations in area 30 and
31 (FIG. 1). Attenuator 110 may be a one cell attenuator or it may
be a spatial modulator. It should be noted that many different
scanner designs can be used to generate a scanned beam, for example
scanners using rotating prisms and acusto-optical scanners.
[0086] Additional potential advantages of a scanner which may be
realized in some embodiments of the invention, include:
[0087] (a) limiting the laser and/or heat damage from nearby
areas;
[0088] (b) providing depth control of the ablation in different
parts of the eye;
[0089] (c) providing percolation rate control in different parts of
the eye;
[0090] (d) when uniform ablation is desired, allowing selection of
uniform depth or uniform tissue thickness;
[0091] (e) varying the scanning speed, intensity, pulse rate and/or
other parameters based on the tissue type. Controller 74 may be
used to simultaneously control laser 52 and scanner 56 to achieve
various desired laser effects; and/or
[0092] (f) controlling the local pulse rate to match the actual
pulse rate of the laser with the local percolation rate and a
desired percolation rate at which the procedure should be
self-limiting.
[0093] FIG. 3B is a schematic illustration of an exemplary
combiner/micro-manipulator 70 for system 50, in accordance with one
embodiment of the invention. As noted above, in some embodiments of
the invention the input beam is scanned, rather than being
restricted to a single spatial location. Thus, combiner 70 is
optionally designed to properly combine the beam with the line of
sight of microscope 58 over an expected range of off-axis positions
of the scanning beam.
[0094] As shown in FIG. 3B, a beam 54 enters combiner 70 and is
optically processed by an optical system 120, which system controls
the focusing of beam 54, so that it will be focused at areas 30 and
31, as required. In one embodiment of the invention, optical system
120 is configured and/or controlled so that beam 54 has the same
focal plane as microscope 58. As will be described below, this can
be achieved manually or automatically.
[0095] The optical path of microscope 58 may be delimited by an
enclosing ring 124.
[0096] Beam 54 is combined with the optical path of microscope 58,
using a beam combining element 122, for example a mirror that is
transparent or semi-transparent to visible light and reflective for
infra-red (or the wavelength of the laser). In an exemplary
embodiment of the invention, a joy-stick 72 or other input means is
provided for rotating beam combiner 122, so that the relative
placement of laser beam 54 and the viewing field of microscope 58
can be controlled. Alternatively, the scanning area is defined
and/or moved using scanner 56, which may require a larger and/or
wider angle beam combiner to be provided. Alternatively or
additionally, scanner 56 is provided as a single unit integral with
combiner 70.
[0097] FIG. 4 is a flowchart 200 of a method of non-penetrating
filtration, in accordance with an exemplary embodiment of the
invention. First, at 202, a flap 26 (FIG. 1) is formed in the
conjunctiva of the eye. At 204, a flap is formed in the sclera 41
and cornea 42. Such flaps may be formed using any method known in
the art, including using a scalpel, a laser and/or a dedicated
cutting tool.
[0098] FIG. 5 is a perspective view of eye 40 showing an exposed
ablation area 30 and 31, in accordance with an exemplary embodiment
of the invention. In one embodiment of the invention, the flaps are
opened so that they unroll in different directions. Thus, when the
flaps are closed, the tip of one flap is under the base of the
other flaps. This may provide a stronger seal. In the embodiment
shown, the two flaps open in opposite directions, however, other
angular relationships may be provided, for example an orthogonal
relationship. Alternatively or additionally, the tip of sclera flap
27 is over sclera 41, for example, so that any swelling or
inflammation will be less likely to affect the lens. Alternatively,
the tip of flap 27 is over cornea 42 or, alternatively, over the
boundary between the sclera and cornea.
[0099] At 205, the tools to be used are calibrated for the ablation
area. In some embodiments, the tools are calibrated before the
start of the procedure and/or periodically recalibrated during the
procedure. Exemplary calibrations include: beam intensity,
scanner/combiner alignment and/or laser focal plane. A laser focal
plane calibration may be performed in conjunction with setting the
microscope focal plane. Alternatively or additionally, a flexible
focal distance combiner is used, which includes lens and/or other
optical elements for varying the focal distance.
[0100] The target area may be shown, for example as a marking on
mirror 122 (FIG. 3B). Alternatively or additionally, a computer
display may be provided showing an image of the eye and an
estimated or imaged position of the laser beam. In some
embodiments, a computer generated display showing, for example,
scanning parameters, is combined with microscope 58, so viewer 62
can view the display via the microscope.
[0101] Depending on the particular implementation, microscope 58
and/or combiner 70 (which may be an integral unit with microscope
58), may or may not be in contact with eye 40 and/or ablated areas
30 and 31.
[0102] As will be described below, in an exemplary embodiment of
the invention, both a percolation zone 220 (FIG. 6 below) for
allowing percolation of the aqueous humor and a reservoir zone 222
(FIG. 6 below) for storing the up-welling humor until it is
absorbed, may be formed. They may be formed with a same scanning
setting, as part of a same scan, or separately. In other
embodiments, only a percolation zone is formed. Typically, these
zones are covered by a tissue flap when the procedure is
completed.
[0103] At 206, a percolation zone 220 is ablated in area 30
overlying Schlemm canal 34 and trabecular meshwork 32. If the
aqueous humor does not percolate (208) the ablation step is
repeated. In one embodiment of the invention, once a percolation is
detected or a minimal percolation rate is detected (both of which
may be manually or automatically detected), the ablation is
stopped. In another embodiment of the invention, ablation is
stopped or slowed down at points where percolation is detected, but
continued at other parts of area 30 and/or area 31. A minimal
percolation zone may be defined, which is smaller than the actual
ablated area of area 30. Thus, the ablation is closed circuit,
i.e., iterative, or open circuit ablation can be practiced as well,
at least for the reservoir, for example based on predefined laser
beam settings.
[0104] Typically, the tissue in area 30 has a varying thickness, by
ablating more at areas where there is less percolation, a uniformly
thin filter area may be defined. Alternatively, a uniform (or other
profile) percolation distribution can be achieved. Also,
percolation-adapted ablation allows a matching of the scanning
parameters to the tissue laser sensitivity. One or more of the
following scanning parameters may be varied over the ablation area,
to control the ablation:
[0105] (a) Spot size. A larger spot size provides a lower
resolution and less energy per unit area. In some embodiments,
non-circular spots are used, for example, elliptical, triangular,
hexagonal and rectangular. Alternatively or additionally, a spot
pattern may be provided. Such a pattern may be continuous, for
example Gaussian or uniform, or discrete, for example,
checkerboard. Exemplary circular spot sizes are between 0.1 mm and
1 mm, for example 0.8 mm.
[0106] (b) Dwell time. By varying the scanning speed, more energy
can be deposited at locations that are not yet percolating and less
energy at locations where no further ablation is desired. An
exemplary dwell time is between 100 .mu.s and 1000 ms, for example
400 .mu.s.
[0107] (c) Beam intensity. This may be controlled, for example, by
modulating the laser source or using attenuator 110, or another
attenuator (uniform or spatially modulating) elsewhere along the
optical path. The attenuators may selectively attenuate only the
ablating beam (and not the optional aiming beam) for example having
frequency selective properties or being having a suitable physical
location. In some cases, the beam may be turned off for part of the
scan. An exemplary source beam intensity is between 5 W and 15 W.
The actual intensity that should be delivered to the eye can depend
on various parameters, for example, the dwell time (and spot size),
the age of the eye tissue, and the type of effect desired, e.g.,
ablation or coagulation. In particular, increasing the beam
intensity can increase the thickness of ablation.
[0108] (d) Beam location and scan pattern. In some embodiments, the
beam scans the entire area, regardless of the effects of the beam.
Alternatively, the beam may skip certain location and/or change the
scan area definitions, on the fly, to match the percolating zones
and/or required ablations.
[0109] (e) Scan path. In some embodiments, the scan path is
selected so that there will be sufficient time to detect
percolation at a location, between repeated ablations of the
location. Alternatively or additionally, the scan path may be
changed responsive to the initiation of percolation at some
locations in the area. Optionally, the scan path overlaps itself,
for example 10%. An exemplary scan path is by rows. Optionally, the
scanning is interleaved, with a greater separation between rows.
The row direction may reverse itself every row.
[0110] (f) Scan shape. Various scan shapes may be used, to achieve
variously shaped percolation and/or reservoir shapes.
[0111] (g) Laser pulse parameters, such as pulse length, pulse
envelope and pulse repetition rate. In some embodiments, a pulsed
laser is used. The laser may generate a pulsed beam or a continuous
pulsed beam may be further temporally modulated. In one exemplary
embodiment, a CW laser is used and modulated to have pulses between
1 .mu.s and 1 ms and a repetition between 1 Hz and 1 kHz.
Alternatively, a continuous beam is provided at the eye. In a
particular example, pulse duration is reduced, in order to reduce
thermal damage.
[0112] (h) Local Pulse Rate. This is a composite of several
parameters and defines the rate at which laser pulses will contact
a certain area, thus also defining the time for percolation between
pulses. By matching the local pulse rate to a desired percolation
rate, the thickness of membrane 48 can be set or at least more
closely approximated.
[0113] Alternatively or additionally to detection percolation using
image processor 68, other feedback mechanisms may be used to
control ablation, set ablation parameters and/or to provide alarm
signals. Image processor 68 is optionally used to detect the
thickness of the sclera and/or the depth of ablation. Several depth
and distance measuring methods are known in the art, for example,
using stereoscopic imaging, or by detecting shadows or changes in
patterns of light that are projected from a side light (not shown).
Alternatively or additionally, an optional dedicated sensor 37
(FIG. 1) is used , for example, for detecting percolation or
measuring the thickness of the sclera or the depth of ablation, for
example, optically or using ultrasonic reflection. A thickness
sensor may also be used prior to the procedure, for example for
mapping (e.g., to set ablation parameters in general or for
different locations).
[0114] Alternatively or additionally, an optional contact sensor 35
(FIG. 1) is used to measure the sclera thickness, for example
timing ultrasonic reflection from the aqueous humor of the eye.
Alternatively or additionally, sensor 35 detects percolation (e.g.,
by detecting flow or moisture) and is located at an area which is
not ablated. Optionally, the contact sensor is manually positioned
so that the laser radiation does not hit it.
[0115] Alternatively or additionally to directly monitoring the
ablation or the percolation, an optional sensor 39 (FIG. 1) may be
used for monitoring the pressure in eye 40. Various types of such
pressure sensors may be used, for example sensors which require
applying pressure to the eye. Possibly, such sensors did not find
use during surgery in previous times, due to fears of a possible
interaction between such pressure (which may be deforming) and the
delicacy of the procedure or the forcing of fluid from the eye. A
potential advantage in accordance with an exemplary embodiment of
the invention is the ability to receive feedback in real-time or
near real-time on the effect of a part of the procedure, so that a
more finely tuned effect on intra-ocular may be achieved.
[0116] When percolation is achieved, it is expected that the
intra-ocular pressure will go down. However, after a time, the
pressure may go up, stay steady, go down or oscillate for a while.
The time until a steady pressure is achieved may be as long as
several weeks or as short as a few minutes. However, it is expected
that for some situations (e.g., initial pressure, type of ablation
pattern, speed of response, degree of response) the behavior of the
pressure can be estimated. Optionally, different changes in
pressure profiles are stored and are used to identify the degree of
percolation under different conditions (e.g., by accumulating a
database of profiles and results). In an exemplary embodiment of
the invention, two types of pressure reductions are distinguished,
an immediate pressure reduction and a long term pressure reduction.
Thus, for example, when percolation first occurs, the pressure is
expected to go down to a lower level. This distinction, may, in
some cases, be a simple modeling of an exponential decrease in
pressure. In some cases, for example, the procedure is stopped when
a reduced pressure 16 mm is achieved, even though a final expected
and desired pressure is 12 mm. In other cases, the procedure may be
stopped at 12 mm, and the pressure will then climb up to 16 mm, for
a steady state final pressure. Optionally, detection of
intra-ocular pressure reduction is used to automatically modify
ablation parameters and/or to stop ablation. For example, the
ablation pattern area may be reduced if pressure reduction is
found. Alternatively, if a pressure reduction is not sufficient,
the ablation pattern may be enlarged and/or pulse or scanning
parameters (e.g., as described herein) changed. In a simple case,
changes in pressure are used to decide if to stop the
procedure.
[0117] The input from the sensor (or imaging system) may be used
manually or automatically, depending on the implementation. For
example, controller 74 may analyze and respond to input form such
sensors automatically. Alternatively or additionally, a user reads
the sensor readings and inputs new parameters into controller 74,
for example using input 76. Alternatively or additionally, a user
enters the sensor reading into the input and controller 74 analyses
the input to determine a response. One potential advantage of such
user intermediate activity is that there is no need to electrically
couple the sensor to the ablation system and any existing sensor
may be used.
[0118] Alternatively or additionally to storing pressure profiles,
ablation rate profiles may be stored, with the understanding that
as percolation initiates and processes, the ablation rate will go
down. Such ablation profiles (e.g., thickness profiles) may be used
to assess the progression of the procedure and/or to indicate alarm
conditions.
[0119] At 210, reservoir 222 (FIG. 6) is optionally created.
Instead of using percolation to detect the reservoir depth, it may
be estimated based on the laser energy deposition or it may be
determined using image processor 68. In some embodiments, reservoir
222 is created while or prior to creating percolation zone 220.
[0120] FIGS. 6A and 6B illustrate a completed percolation (220) and
reservoir (222) system, from a side and a top view, in accordance
with an exemplary embodiment of the invention.
[0121] FIG. 6A shows the situation after flaps 26 and 27 are
closed. FIG. 6B is a top view, with the flaps shown as a dotted
line.
[0122] As shown, reservoir 222 and percolation zone 220 have
different geometries, which can include different shapes, sizes
and/or depths. In an exemplary embodiment, percolation zone 220 is
3.times.3 mm and reservoir 222 is 5.times.3 mm. Alternative
exemplary sizes for percolation zone 220 are between 2 and 5 mm by
between 2 and 5 mm. Alternative exemplary sizes for reservoir 222
are between 3 and 5 mm by between 3 and 5 mm. The actual sizes of
the zones may be fixed. Alternatively, one or both sizes decided
ahead of time based on patient characteristics, for example,
eye-size, age and intra-ocular pressure. Alternatively or
additionally, the actual sizes may be decided during the procedure,
for example, based on the percolation rate. Alternatively or
additionally, the sizes of percolation zone 220 and/or reservoir
222 may be adjusted (up or down) in a later procedure.
[0123] However non-rectangular shapes can be provided, for example,
round, elliptical or polygonal with, for example, between 3 and 10
facets. In particular, both convex and concave forms may be
provided, for example to provide different perimeter-area ratios
for reservoir 222 and/or percolation zone 220. Alternatively or
additionally, at least part of one of the zones may be provided as
a plurality of elongated zones.
[0124] Alternatively to contiguous reservoir and percolation zone,
the two may be separated by one or more channels, for example a
channel ablated in the sclera.
[0125] In some cases, ablation may cause charring of the eye or
deposition of debris. Optionally, such charring is cleaned away
using fluid or a wipe.
[0126] Optionally, prior to closing the flaps, a spacer is insert
to maintain reservoir 222 and/or percolation zone 220 open (212),
at least until the spacer is absorbed, as some spacers are formed
of a bio-absorbable material. Exemplary spacers are:
[0127] (a) AquaFlow by Staar inc., formed of collagen;
[0128] (b) SK-Gel by Corneal Co., formed or reticulated hyaluronic
acid;
[0129] (c) Hydrogel implants of various designs; and/or
[0130] (d) Scleral implants formed of left over or harvested pieces
of ocular tissue.
[0131] Alternatively or additionally to a spacer, an anti-metabolic
material may be provided at the ablated area, to retard tissue
ingrowth. Exemplary materials include: Mitomycin, typically
contact-applied as a damp sponge for 2-3 minutes and
5-Fluoro-Uracil (5FU), typically applied as a series of
sub-conjectival injection after the procedure.
[0132] At 214, the flaps are closed and sealed, for example using a
laser, adhesive or by sewing.
[0133] Alternatively to scanning, in one embodiment of the
invention, a large spot size is used, to cover the entire ablation
area. Optionally, ablation will stop at portions of the ablated
area that percolate, for example by a mechanism of the laser light
being absorbed by the percolating aqueous humor only at the
sufficiently ablated locations.
[0134] In another alternative to scanning, the procedure may be
performed free-hand. Optionally, an integral scanner is provided in
the probe. An aiming beam, which may be scanned or not, may be used
to show the scan boundaries.
[0135] In an exemplary embodiment of the invention, the
self-limiting behavior of the laser interaction with the sclera is
used as a control feature or a safety feature, depending on the
laser and on the degree of certainty. In one example, the
self-limiting behavior is used as a control feature. The laser is
set to have an ablation depth (e.g., power, pulse length) equal to
the expected percolation rate when a desired membrane is achieved.
This percolation rate may depend, for example, on the intra-ocular
pressure and/or on other parameters, such as results from a
previous or a same operation on the patient. Another possible
setting is a matching between ablation depth in sclera and in
fluid. This setting may vary, for example, if the sclera or
intra-ocular fluid are dyed or otherwise have significantly
different absorption at the laser wavelength. Optionally, the scan
settings are modified to provide a local pulse rate that matches
the expected percolation rate. In an exemplary embodiment of the
invention, the power setting is 3 J/cm.sup.2 and the pulse duration
is 1 ms. Higher power, such as 10 or 20 J/cm.sup.2 at this pulse
duration will provide a greater ablation depth. Exemplary durations
are thus between 1-2000 .mu.s, for an isotopic CO.sub.2 laser.
Exemplary power levels are between 2.5 and 50 J/cm.sup.2. In
contrast, an Erbium:YAG can work at 1.5 J, but has undesirable
self-limiting behavior. The exact power setting may depend of
course on the exact spectral wavelength of the laser and/or on the
absorbency characteristics of the sclera. Also, the sclera and/or
the percolating fluid (e.g., the eye) may be dyed to have desired
absorbency characteristics.
[0136] The procedure as described above is applied. Once the
percolation is fast enough, the ablation effectively stops and the
operator can stop the laser. Alternatively, the automatic vision
system is used to stop the procedure once it is determined that no
further ablation of sclera is being achieved.
[0137] In a safety method, the same setting settings are applied,
However, the operator does not trust the system or is worried that
thermal damage may be caused by repeated ablation of fluid.
Instead, the operator sets the ablation depth and ablates until he
sees fluid and then ablates at a slower rate (e.g., using less
often applied manual "zap" instructions) and/or at a lower ablation
thickness setting, until the percolation rate appears to be
correct. If the operator makes a mistake, the ablation should not
penetrate through the sclera, as it is self-limiting.
[0138] It should be noted that the same procedure, possibly with
different parameters may be applied to a wide range of patients.
These patients may be characterized, for example, by different
percolation rates and/or different target percolation rates. For
example, the non-penetrating filtration procedure may be applied as
a precautionary measure or in patients with slightly elevated
intra-ocular pressures, such as pressures, between 14 mmHg and 21
mmHg or below 30 mmHg.
[0139] FIG. 7 illustrates an exemplary protective framework 300, in
accordance with an embodiment of the invention. Framework 300 is
optionally attached to microscope 58 and blocks laser light from
reaching outside of the ablation areas 30 and 31 and/or a safety
zone defined around them. Alternatively or additionally, framework
300 may be attached to the patient. As shown, framework 300
comprises an attachment extension 302 for attaching the framework
and a frame 304 defined, in this embodiment, by four bars. These
bars may be wider than shown and/or may have a curtain attached to
them for example a disposable adhesive (to the framework) curtain.
The required focal distances of the procedure are optionally set
using framework 300. A distance adjustment screw 306 may optionally
be provided. Alternatively or additionally, framework geometry
defining screws 308 may be provided, to control the shape and/or
size of the framework and, thus, the ablateable zone. In some
embodiments, frame 300 is not rectangular, for example being formed
of a pliable wire. Alternatively or additionally, frame 300 may be
semi-transparent, but not to except to beam 54. In one example,
frame 700 comprises a holder, for example a clip, for a transparent
plate the defines the laser action area.
[0140] FIGS. 8A and 8B illustrate two alternative exemplary eye
protectors in accordance with some embodiments of the
invention.
[0141] FIG. 8A shows an aperture type protector 400, comprising a
body 402 that blocks laser light and an aperture 404 which passes
laser light. In one embodiment of the invention, body 402 is
flexible and adhesive, for example being a silicon rubber sheet.
Optionally, body 402, when attached to eye 40, maintains flaps 26
and 27 open. Alternatively to being flexible, body 402 may be rigid
or plastically deformable. Alternatively to adhesive, other
attachment methods, such as suturing, vacuum and/or self adhesion
to the eye surface based on mechanical properties of the eye
surface and/or body 402, may be used instead. Protector 400 may be
disposable or sterilizable. Optionally, aperture 404 (or window
410, below) defines the shape of the ablation areas and/or shape of
the flaps, for example if the flaps are cut using a laser.
[0142] FIG. 8B shows a window type protector 410 having a body 412
which can be the same as body 402. However, instead of an aperture
404, a window 414 may be provided for selective transmission of
laser light. As shown, window 414 may protrude, for example towards
the microscope, optionally to provide contact with the optical path
and/or towards the eye, for example fitting into areas 30 and 31.
Alternatively, a flat window may be provided. In an exemplary
embodiment of the invention, window 414 is formed of a laser
sensitive material, that turn opaque after a certain amount of
energy is deposited in it, preventing inadvertent damage to the
eye.
[0143] Alternatively, protector 410 may be attached to the
microscope, for example using adhesive or being formed as a slide
that can be coupled to the microscope. Alternatively to a slide,
movable shutters are provided to limit the possible positions of
the laser beam on the eye.
[0144] It will be appreciated that the above described methods of
selective ablation of sclera and corneal tissue may be varied in
many ways, including, changing the order of steps and the types of
tools used. In addition, a multiplicity of various features, both
of method and of devices have been described. In some embodiments
mainly methods are described, however, also apparatus adapted for
performing the methods are considered to be within the scope of the
invention. It should be appreciated that different features may be
combined in different ways. In particular, not all the features
shown above in a particular embodiment are necessary in every
similar embodiment of the invention. Further, combinations of the
above features are also considered to be within the scope of some
embodiments of the invention. Also within the scope of the
invention are surgical kits which include sets of medical devices
suitable for performing a single or a small number filtration
procedures. When used in the following claims, the terms
"comprises", "includes", "have" and their conjugates mean
"including but not limited to".
[0145] It will be appreciated by a person skilled in the art that
the present invention is not limited by what has thus far been
described. Rather, the scope of the present invention is limited
only by the following claims.
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